A fuel cell has been proposed as a clean, efficient and environmentally responsible power source for electric vehicles and various other applications. Individual fuel cells can be stacked together in a series to form a fuel cell stack for various applications. The fuel cell stack is capable of supplying a quantity of electricity sufficient to power a vehicle. In particular, the fuel cell stack has been identified as a potential alternative for the traditional internal-combustion engine used in modern automobiles.
One type of fuel cell is the polymer electrolyte membrane (PEM) fuel cell. The PEM fuel cell includes three basic components: an electrolyte membrane; and a pair of electrodes, including a cathode and an anode. The electrolyte membrane is sandwiched between the electrodes to form a membrane-electrode-assembly (MEA). The MEA is typically disposed between porous diffusion media (DM), such as carbon fiber paper, which facilitates a delivery of reactants, such as hydrogen to the anode and oxygen to the cathode. An MEA and DM preassembled together with a subgasket for the separation of reactant fluids is known as a unitized electrode assembly (UEA).
In the electrochemical fuel cell reaction, the hydrogen is catalytically oxidized in the anode to generate free protons and electrons. The protons pass through the electrolyte to the cathode. The electrons from the anode cannot pass through the electrolyte membrane, and are instead directed as an electric current to the cathode through an electrical load, such as an electric motor. The protons react with the oxygen and the electrons in the cathode to generate water.
The electrolyte membrane is typically formed from a layer of ionomer. The electrodes of the fuel cell are generally formed from a finely divided catalyst. The catalyst may be any electro-catalyst that catalytically supports at least one of an oxidation of hydrogen or methanol and a reduction of oxygen for the fuel cell electrochemical reaction. The catalyst is typically a precious metal such as platinum or another platinum-group metal. The catalyst is generally disposed on a carbon support, such as carbon black particles, and is dispersed in an ionomer.
The electrolyte membrane, electrodes, DM, and subgasket, for example, in the form of the UEA, are disposed between a pair of fuel cell plates. The pair of fuel cell plates constitutes an anode plate and a cathode plate. Each of the fuel cell plates may have a plurality of channels formed therein for distribution of the reactants and coolant to the fuel cell. The fuel cell plate is typically formed by a conventional process for shaping sheet metal such as stamping, machining, molding, or photo etching through a photolithographic mask, for example. In the case of a bipolar fuel cell plate, the fuel cell plate is typically formed from a pair of unipolar plates, which are then joined to form the bipolar fuel cell plate.
It is known to provide the fuel cell plates and the subgasket of the UEA with datum holes. During assembly of the fuel cell stack, the fuel cell plates are positioned over datum pins. The datum pins are typically formed from metal and disposed through the datum holes to properly align the fuel cell plates. The datum pins can undesirably deform, for example, bend or flare the metal around the plate datum holes during the assembly. The deformed metal around the datum holes of the fuel cell plates can contact an adjacent fuel cell plate when the fuel cell stack is assembled, and thereby cause electrical shorting of the fuel cell stack.
There is a continuing need for a subassembly for a fuel cell stack that minimizes an opportunity for datum holes of a fuel cell plate to become deformed upon contact with datum pins during assembly of the fuel cell stack.